Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$233.44	5.546%	$246.3866	$246.39	$246.40	$246.40
Purchase #2	$10.92	7.334%	$11.7209	$11.72	$11.70	$11.70
Purchase #3	$63.90	4.250%	$66.6158	$66.62	$66.60	$66.60
Purchase #4	$33.45	12.606%	$37.6667	$37.67	$37.65	$37.70
Purchase #5	$211.95	12.673%	$238.8104	$238.81	$238.80	$238.80
Purchase #6	$139.37	9.367%	$152.4248	$152.42	$152.40	$152.40
Purchase #7	$243.80	9.231%	$266.3052	$266.31	$266.30	$266.30
7 purchase totals =	$936.83		$1,019.9304	$1,019.94	$1,019.85	$1,019.90